Memory device have many trade offs. Memory which is fast may be expensive. Memory which is slow may be inexpensive. As the memory demands of modern applications exceed the physical capacity of customer systems, paging operations to the hard drive quickly make the system and applications appear slow and unresponsive, particularly when switching between tasks or users. In an ideal computer, all the memory would be as fast as possible, but such a computer would be too expensive to be realistic. In addition, there are some applications where cheap, long term storage is all that is needed. As a result, computers have a variety of memory from ultra fast memory close to the processor to slower memory such as disk based memory. In addition, computers have the ability to add more and different types of memory such as portable hard drives, floppy disks and flash memory devices. Each of these devices have performance and wear characteristics which may be maximized.